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PRCI PR-201-927
- Criteria for Dent Acceptability of Offshore Pipelines
- Report / Survey by Pipeline Research Council International, 07/01/1992
- Publisher: PRCI
$198.00$395.00
L51671e
Stress Engineering Services Inc.
Need: Extensive research has provided an understanding in the behavior of pipelines subjected to mechanical damage. The presence of a gouge or the combination of a gouge and a dent has been proven detrimental to the burst strength of pipelines. The research has also revealed that plain smooth dents, in the absence of a defect, do not significantly reduce the burst strength of pipelines. On the other hand, plain dents locally increase the pipe stress due to pressure. Thus, fatigue failures from dents can occur from normal operating pressure fluctuations in the lines over a period of time
Benefit: This report documents the testing and analysis work done at Stress Engineering Services to establish the effects of pipeline dents (without gouges) under cyclic internal pressure loading. The work consisted of several sub-tasks. First, operators were surveyed regarding the expected dent shapes and failures from dents that had been experienced. Secondly, a full scale test program utilizing 12-3/4" pipe was carried out. In this program eight pipes, each 20' long with diameter/thickness ratios of 18-50, were subjected to three dents each of various sizes and pressure cycled until failure or until 50,000 to 70,000 equivalent cycles of 0 - 1200 psi pressure was achieved. Next, elastic finite element analysis was utilized to determine the significance of dent shapes and lengths. Finally plastic finite element analysis was utilized to determine analytically the stress to pressure ratios so that a fatigue analysis could be done.
Result: The results indicate that plain smooth dents less than 5% of the diameter for pipe with a diameter to thickness of less than 30 are not a problem for normal pipeline service. Other dents may or may not be a problem depending upon the pressure cycles encountered in the pipeline. Plain dents are probably not a concern for normal gas line service. An analytical procedure was developed to predict the fatigue life of a pipeline subjected to any combination of pressure cycles and any specified depth of plain dent and any pipeline diameter to the thickness ratio.
Stress Engineering Services Inc.
Need: Extensive research has provided an understanding in the behavior of pipelines subjected to mechanical damage. The presence of a gouge or the combination of a gouge and a dent has been proven detrimental to the burst strength of pipelines. The research has also revealed that plain smooth dents, in the absence of a defect, do not significantly reduce the burst strength of pipelines. On the other hand, plain dents locally increase the pipe stress due to pressure. Thus, fatigue failures from dents can occur from normal operating pressure fluctuations in the lines over a period of time
Benefit: This report documents the testing and analysis work done at Stress Engineering Services to establish the effects of pipeline dents (without gouges) under cyclic internal pressure loading. The work consisted of several sub-tasks. First, operators were surveyed regarding the expected dent shapes and failures from dents that had been experienced. Secondly, a full scale test program utilizing 12-3/4" pipe was carried out. In this program eight pipes, each 20' long with diameter/thickness ratios of 18-50, were subjected to three dents each of various sizes and pressure cycled until failure or until 50,000 to 70,000 equivalent cycles of 0 - 1200 psi pressure was achieved. Next, elastic finite element analysis was utilized to determine the significance of dent shapes and lengths. Finally plastic finite element analysis was utilized to determine analytically the stress to pressure ratios so that a fatigue analysis could be done.
Result: The results indicate that plain smooth dents less than 5% of the diameter for pipe with a diameter to thickness of less than 30 are not a problem for normal pipeline service. Other dents may or may not be a problem depending upon the pressure cycles encountered in the pipeline. Plain dents are probably not a concern for normal gas line service. An analytical procedure was developed to predict the fatigue life of a pipeline subjected to any combination of pressure cycles and any specified depth of plain dent and any pipeline diameter to the thickness ratio.
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